2. Yeah, a "douche nozzle" goes into a woman's vagina. So does a "dick head" - same use of the terms.

It isn't because it goes into a woman's vagina, both just happen to do so (well, not ALL dick heads get a chance), but dick weed (no idea what that might actually mean), douche bag, ass wipe, fuck head, fuck stick, corn dog, needle dick the bug fucker, and other similar terms are just variations of less creative insulting terms.